ffs

FFS(3)                     Linux Programmer's Manual                    FFS(3)



NAME
       ffs, ffsl, ffsll - find first bit set in a word

SYNOPSIS
       #include <strings.h>

       int ffs(int i);

       #include <string.h>

       int ffsl(long int i);

       int ffsll(long long int i);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       ffs():
           Since glibc 2.12:
                   _XOPEN_SOURCE >= 700
                   || ! (_POSIX_C_SOURCE >= 200809L)
                   || /* Glibc since 2.19: */ _DEFAULT_SOURCE
                   || /* Glibc versions <= 2.19: */ _BSD_SOURCE ||
               _SVID_SOURCE
           Before glibc 2.12:
               none
       ffsl(), ffsll():
           Since glibc 2.27:
                   _DEFAULT_SOURCE
           Before glibc 2.27:
                   _GNU_SOURCE

DESCRIPTION
       The ffs() function returns the position of the first (least
       significant) bit set in the word i.  The least significant bit is
       position 1 and the most significant position is, for example, 32 or 64.
       The functions ffsll() and ffsl() do the same but take arguments of
       possibly different size.

RETURN VALUE
       These functions return the position of the first bit set, or 0 if no
       bits are set in i.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       ┌───────────────────────┬───────────────┬─────────┐
       │Interface              Attribute     Value   │
       ├───────────────────────┼───────────────┼─────────┤
       │ffs(), ffsl(), ffsll() │ Thread safety │ MT-Safe │
       └───────────────────────┴───────────────┴─────────┘
CONFORMING TO
       ffs(): POSIX.1-2001, POSIX.1-2008, 4.3BSD.

       The ffsl() and ffsll() functions are glibc extensions.

NOTES
       BSD systems have a prototype in <string.h>.

SEE ALSO
       memchr(3)

COLOPHON
       This page is part of release 5.06 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



GNU                               2017-09-15                            FFS(3)